This invention relates to reagents and methods for targeting a diagnostic and/or therapeutic agent to a focus of pathogenic infection by using as the targeting vehicle an antibody conjugate that specifically binds to one or more accessible epitopes of the pathogen or of a pathogen-associated antigen.
Drug therapy against pathogens is conventionally effected by means of systemic administration the drug in order to achieve a blood level which toxic to the pathogen wherever it is harbored in the body. Thus, a certain blood level is necessary in order to provide the proper concentration of the drug at the site of infection. This requires high doses and often does not achieve the desired toxicity without resulting in unacceptably adverse side-effects to the patient, since many of these drugs have general cytotoxic properties.
The development and description of murine monoclonal antibodies (MAbs) against infectious organisms has been the subject of a number of reviews (eg., M. C. Harris et al., Indian J. Pediatr., 54:481-488, 1987; S. Cohen, Brit. Med. Bull., 40:291-296, 1984; R. A. Polin, Eur J. Clin. Microbiol., 3:387-398, 1984; R. C. Nowinski et al., Science, 219:637-644, 1983; Part V, Monoclonal Antibodies to Microorganisms, Chapters 17-20, inclusive, In: R. H. Kennett et al., (eds.), Monoclonal Antibodies. Hybridomas: A New Dimension in Biological Analyses, New York and London, Plenum Press, 1980, pp. 295-362). These papers, and others in this area, have been concerned with the use of such monoclonal antibody reagents for improved diagnostic tests for the infectious microorganisms, including bacteria, viruses, protozoa and helminths.
It has been proposed that these MAbs can be used as such for both the diagnosis and therapy of certain bacterial diseases, such as group B streptococcal infections (Harris, cited above), but exclusively as diagnostic agents in viral diseases (Harris, cited above). In the case of group B streptococcal infections, MAbs were used in rodents to treat the infection, and it was found in these limited trials that only when the MAbs were infused early after infection was an effect achieved; at 6 hours or later, no survival of the animal occurred (Christensen et al., Pediatric Res., 18:1093-1096, 1984). In the case of malarial parasites, it has been shown that the Fab fragments of a monoclonal antibody directed against the surface coat of malaria sporozoites is active in protecting mice against malarial infection, indicating that it blocks attachment of sporozoites to host receptor cells (P. Potocnjak et al., J. Exp. Med., 151:1504-1513, 1980). This further indicates, since it is achieved by the immunoglobulin molecule lacking the Fc portion, that the protective antibody action is independent of complement or cells.
These animal experiments indicate that early infections can be affected by the use of organism-specific MAbs in well-controlled laboratory experiments involving certain bacteria and parasites. Despite these reports a number of years ago, MAbs have not been shown to have a therapeutic role in infectious diseases in humans. One major reason has been that such MAbs exert a protective action only in specific, usually early stages of infection, being less able to interact with the infectious organisms when they have disseminated into tissue reservoirs that are less accessible to interaction with the injected MAbs. Use of such MAbs to form therapeutic conjugates is not suggested by the references.
A need therefore exists for a method of targeting a diagnostic agent, e.g., an imaging agent, or a therapy agent, e.g., a drug or radioisotope, to a focus of infection with higher efficiency and an enhanced therapeutic index to permit more effective diagnosis and/or treatment of the infection.